Check valves or their equivalents have been probably known since the development of the first fluid displacement pumps. Moreover, ink-jet printers have been commercially available since at least the late 1980's, and their general construction is also well known, being the subject of numerous patents world-wide.
Nevertheless, developing a simple, low cost, dependable check valve for the ink pumps used in these printers has proven to be a difficult task. One problem has been to develop a check valve that is as insensitive as possible to any strain that develops during manufacture and thereafter. Such strain can cause the check valve to fail to close and to permit the back flow of ink out of the pump chamber, resulting first in the loss of pump efficiency and ultimately in the failure of the check valve to function. Such strain can be caused by numerous factors including an externally applied mechanical load, mechanical interference, chemical attack by the ink causing either shrinkage or swelling, thermal excursion, and continued polymer crystallization after fabrication.
Other problems include check valves opening too slowly or not sufficiently enough so the pump chamber fills too slowly with ink, causing the speed of the printer to diminish and printing through-put to become hampered. Another problem has been designing a check valve that can be pre-loaded shut against its valve seat so that the check valve is insensitive to the actuation speed of the pump. The preload is achieved by axially deforming the center portion of an inexpensive, die cut disk which costs an order of magnitude less than a thermoset part with three dimensional detail derived from compression molding or similar processes.
It will be apparent from the foregoing that although there are many processes and apparatus for transporting ink in ink-jet printers, there is still a need for a check valve in an ink pump that is dependable, low cost, and simple in design.